Modulated transmitter



Jun@ 1l., 1943. R. H. GEORGE MODULATED TRANSMITTER Filed Oct. '7, 1939Almmw mdx Patented June 1, 1943 UNITED STATES asians PATENT OFFICE.

MQDULATED TRANSMITTER Roscoe H. George, West Lafayette, Ind., assignorto Radio Corporation of America, a corporation of Delaware 8 Claims.

This invention relates to transmitters and particularly to modulatedradio frequency transmitters of quasi-optical wave characteristics. Moreparticularly the invention relates to the modulation of twoultra-high-frequency transmitters by a. single oscillator so arrangedthat each of the two transmitters is modulated either alternately orsequentially or in a predetermined recurring order.

In accordance with one preferred form of the invention, the tuned radiofrequency transmitters have their output electrode elements suppliedthrough the tank circuit of an oscillator, which oscillator mayconveniently be of the scalled push-pull type so that alternately firstone of the transmitters and then the other has its output electrodeelement potential raised to such a value that oscillations may takeplace. Such a transmission system nds particular use in radio navigationaids for aircraft, such as disclosed by co-pending application SerialNo. 198,888, filed by Roscoe H. George on March 30, 1938 for aninvention relating to an Electronic indicating device which issued as U.S. Patent 2,216,707 on October 1, 1940. While the present invention isapplicable to a system of the general type disclosed by the aforesaidpending application, its use is not limited to such a system but, to thecontrary, the present invention may be used wherever it is desired tohave two transmitters modulated alternately by a single frequency.

The present invention thus affords much greater efficiency in modulationby its circuit arrangement and at the same time it provides both f ofquarter wave length transmission lines for ,Y

both the control electrode and output electrode (frequently termed gridand plate) circuits of the transmitter tubes. Accordingly, it is one ofthe objects of this invention to provide a pair of highly stabilizedultra-high-frequency oscillators which shall be modulated alternately bya single oscillator.

Another object of the invention is to provide a simplified modulatingcircuit which shall be more eicient and more easily maintained inoperating condition than modulated systems hitherto used.

A further object of the invention is to provide a highly stabilized highfrequency oscillator of simple form which shall be capable of having itsoscillatory energy easily abstracted and fed to an output circuit whichmay comprise a directive antenna array, for example.

Other objects of the invention will become apparent upon reading thefollowing detailed discussion taken together with the drawing in whichFigure 1 shows in schematic form the circuit arrangement of two radiofrequency transmitters together with their output circuits and theantenna array connected to each, as well as a single push-pulloscillator which serves to modulate the two transmitters; while Figure 2shows some of the constructional 'features of the quarter-wavetransmission line tuned circuit used in the output (plate) and controlelectrode (grid) circuits of the transmitter tubes.

Turning now to Figure 1, the transmitter tubes and 3 have their outputelectrode (anode) elements l5 and 35, respectively, connected to thecenter conductors 2T and 4l, respectively, of the tuned quarter-wavetransmission lines I9 and 38, respectively. The control electrodes(grids), i3 and 33, respectively, of tubes l and 3 are connectedsimilarly to the inner conductors 23 and 43 of the tuned quarter-wavetransmission line circuits Il and 31 respectively. Bias for the controlelectrodes I3 and 33 is provided by the resistors and 85, respectively,which have their common junction point connected to ground, and thecapacities 6l and 8l, which are in parallel with resistors 65 and 85,which establish the desired time-constant control circuit, are providedby the construction of the quarter-wave length transmission lines, asshown in detail in Figure 2, herein to be further described.

Referring now to the constructional features of Figure 2, the outermetal cylinder 59 is secured to a metal plate member E55, by brazingthereto, for example. The inner conductor E51 may likewise be secured(for example, by soldering, brazing or threading) into this same metalplate |55. The metal plate is fastened to a metal chassis l5! (forexample by screws itil) which are insulated from both the plate |55 andthe chassis l5l. Between the plate |55 and the chassis I 5| is a sheetof dielectric material |53, which may be mica,Y glass, enamel, ceramicor other suitable material, so that the end plate |55 o1' thetransmission line, together with the chassis |5|, constitutes acondenser. The capacity of this condenser, naturally, is determined bythe thickness of the insulator or dielectric sheet |53 and the area ofthe end plate. The condenser formed by this construction isconventionally represented in Fig. 1 by the condensers 61 and 81 for thecontrol electrode tuned transmission line, while for the outputelectrode transmission lines, the elements 63 and 83 (formed preferablyby the same construction) form a part of the tuned transmission lines.

Electronic emitting cathodes II and 3| for the tubes I and 3 aresupplied by heating current (e. g. from a 60 cycle power supply)connected to the terminals I09. The actual voltage at terminals |09 mayvary in accordance with the type of tubes used. In order to preservebalance in the heating circuits at exceedingly high frequencies, asymmetrical array of chokes 69, 89, 95 and 91 are provided in thecathode circuit. In general, in order to obtain optimum operatingconditions, it is desirable to have some control of the heating of thecathodes and this is provided by the variable resistors |05 and |01which regulate the actual potential supplied each of the cathodeelements II and 3|. To preserve the symmetry, therefore, between theradio frequency chokes 95 and 91, there is condenser 99 across which twocondensers I I and |03 are connected in series. From the commonconjunction point of the condensers IOI and |03 a ground connection isprovided. It will thus be noted that with respect to radio frequencycurrent which might pass through the chokes 69, 89, 95 and 91, there is'preserved nevertheless a symmetrical arrangement so that nointer-action can take place in the cathode circuits of the tubes I and3.

The anodes I and 35 of tubes I and 3, respectively, are connectedthrough inductance 93 to terminal |00 to which is connected a source ofvoltage (marked plus B). The terminal |00 is connected to the mid-tap ofthe inductance 93 across which inductance is placed a tuning capacitor9|. The combination of the condenser 9| and the inductance 93 forms atuned resonant circuit I9. From each end of the center tapped inductance93 a connection is made to the plate or anode elements 51 and 11 oftubes 5 and 1, respectively. The cathodes 53 and 13 of these two tubesare connected together and maintained at the established groundpotential by suitable conl nection. The electronic emitting cathodeelements are heated by heaters 5I and 1I, respectively, while bias forthe control electrodes 55 and is obtained by the use of resistors 59 and19, respectively. Feedback from the plate circuit to the controlcircuits is obtained by the crossconnected condensers 6I and 8|respectively.

For the generation of oscillations in the ultrahigh-frequencytransmitting tubes and 3, these tubes may be of the type of tube knownin the art as the W. E. 316-A, since a tube of this type is soconstructed as to provide minimum inner electrode capacity and minimumlead inductance. Tubes of the type known as the RCA 53 may be used forthe modulator tubes 5 and 1. The oscillating energy may be fed to theoutput circuit, as shown in Figure l, by using open-ended quarterwavetuned transmission lines III and I 3|, respectively. In practice, theopen end of the tuned transmission line I|I is positioned in registerwith the open end of tuned transmission line I9 and spaced therefrom adistance of the order of 3/4 to 1 inch. The spacing is not critical butwhen the transmitters operate on a frequency of 400 megacycles, it isfound that the spacing thus mentioned provides suiiicient transfer ofenergy to the outside circuit which comprises a directive antenna array,of which one di-pole I23-I25 is shown. For effective feeding of theantenna, a coaxial transmission line I1 is provided in which the innerconductor I2I is connected to the inner conductor I I5 of the tunedtransmission line I I.

The distance from the end plate at which the inner conductor I 2| isconnected to the inner conductor |I5 is not critical but may be on theorder of 1/2 inch to 2 inches, which, in practice. has been found toprovide the optimum transfer of energy within these limits. The outerconductor I|9 of transmission line |I1 is connected to the outerconductor II3 of the coupling tuned transmission line III.

At the output end of the transmission line the outer conductor I|9 isconnected to one-half of the di-pole I 25 while the inner conductor isconnected to the other di-pole |23. A similar set of connections isprovided for the other plate circuit 39 on tube 3 and serves to feed thedi-pole comprising the two members |43 and |45.

Where the modulated pair of transmitters is used in connection with theradio beam landing device, described and referred to above in mycopending application, the di-poles I 23-I25 may be vertically polarizedwhile the di-poles H13-|45 may be horizontally polarized. Thus it willbe appreciated that for each half cycle of the oscillator, whosefrequency is determined by the resonant frequency of the tuned circuitI9, there first will be radiated vertically polarized waves and thenhorizontally polarized waves.

By using quarter-wave length tuned transmission lines in both thecontrol electrode (grid) and output (anode or plate) circuit of each ofthe tubes and 3, high Astability results since these circuits have anexceedingly high Q, that is, the ratio of inductance to resistance ofthe tuned circuit is very large. The resulting oscillator is, therefore,highly stabilized with respect to frequency. This is particularlydesirable in View of the fact that the voltage supplied by the plates I5and varies over wide limits for a range substantially equal to twice thevoltage supplied to the terminal point |00 and marked plus B.

It will be readily appreciated that unless such tuned transmission linesare used, the wide variation in value of plate Voltage would not producea stabilized frequency, but rather, the output energy from thetransmitter would include frequency modulated oscillations as well asamplitude modulation provided by the push-pull oscillator embodying thetubes 5 and 1. However, with the arrangement provided by the invention,even though the voltage at each of the tubes and 3 at alternate 1/2cycles decreases below the point at which oscillations may bemaintained, nevertheless the frequency emitted from the antenna isstable.

It will thus be appreciated that the present invention provides twotransmitters modulated by the same modulator in which there is a minimumnumber of circuit elements, yet which provides substantially modulationfor each of the transmitters so that the over-all operating eiliciencyis considerably higher than those modulating systems known prior.

It is further to be noted that considerable simplicity is achievedWithout the loss of stability of frequency by applicants arrangementsince it is unnecessary to resort to the usual quartz crystal controlledoscillator, together with an intervening amplifier, to drive or controlthe stability of transmitting tubes I and 3.

While the invention has been described for use in connection with radiocontrol of aircraft, it will be readily appreciated that the inventionis not limited to this particular use but may be used in such systems asultra high frequency radio relays Where it is desired to providetransmitters for operating tubes in different directions and at the sametime to provide a pilot frequency for automatic volume control of thelight.

Having described my invention, what I claim is:

1. Transmitting apparatus comprising a pushpull oscillator, a first anda second transmitter, a horizontally polarized antenna system connectedto said rst transmitter, a vertically polarized antenna system connectedto said second transmitter, a source of energy, and common means toenergize said oscillator and said transmitters from said source and tomodulate said transmitters alternately by said oscillator.

2H Transmitting apparatus comprising a pushpull oscillator having aresonant circuit, a rst stabilized high-frequency transmitter, a secondstabilized high-frequency transmitter, a source of energy, means toenergize said oscillator from said source, and means including saidresonant circuit for energizing said rst and said second transmittersfrom said source.

3. Transmitting apparatus comprising a pushpull thermionic oscillatorhaving two output electrodes, a tuned resonant circuit connected betweensaid output electrodes, a source of energizing voltage connected to thetuned circuit, two independent thermionic oscillators each having anoutput electrode, a connection from one of the output electrodes of oneof said independent oscillators to the junction point of said tunedcircuit and one of the output electrodes of the pushpull oscillators, aconnection from the output electrode of the other independent oscillatorto the junction point of the tuned circuit and the other of said outputelectrodes of said push-pull oscillator, and means to derive outputenergy from each of the independent oscillators.

4. Transmitting apparatus comprising a first tuned grid-tuned platethermionic oscillator, a second tuned grid-tuned plate thermionicoscillator, a push-pull thermionic oscillator having a tuned outputcircuit, connections from each of said tuned grid-tuned plateoscillators to the tuned output circuit, and means to energize thepush-pull oscillator and two independent oscillators through saidconnections from a single source of energy.

5. Transmitting apparatus comprising a first tuned grid-tuned plateoscillator, said tuning being provided by open-end quarter wave lengthtransmission lines, an open-end quarter Wave length transmission linecoupled to the tuned plate, means connecting said coupled transmissionline to a vertically polarized antenna array, a second tuned grid-tunedplate oscillator having open-end quarter wave-length tuned transmissionlines, an open-end quarter Wave-length transmission line coupled to saidtuned plate, means connecting said second named coupled transmissionline to a horizontally polarized antenna array, a push-pull oscillator,and means including a single source of energy potential and connectionsfrom said push-pull oscillator to each of the tuned plate of the saidrst and second oscillators for energizing said rst, said second and saidpush-pull oscillator.

6. A transmitting system comprising a rst independent oscillator and asecond independent oscillator, each of a predetermined frequency, athird oscillator having a resonant circuit, a single source of energy,connections from said resonant circuit of said third oscillator to saidfirst and said second oscillators, and means including a connection fromsaid source of energy to said resonant circuit for energizing said thirdoscillator and for energizing said first and said second oscillatorsthrough said first named connections.

'7. In a radio beam landing system, the method of transmitting waveenergy representative of spatial locations, Which comprises the steps ofproducing wave energy of a first predetermined frequency, producing waveenergy of a second predetermined frequency, producing wave energy of athird predetermined frequency, and alternately modulating and radiatingthe produced energy of the first predetermined frequency in a givenplane of polarization and the produced energy of the secondpredetermined frequency in a plane of polarization perpendicular to thegiven plane of polarization, said planes of polarization beingrepresentative of the spatial location of the radiation of the waveenergy.

8. Transmitting apparatus for a radio beam landing device comprising apush-pull oscillator, a rst transmitter, a second transmitter, each ofsaid transmitters having independent frequency-determining elementsserving to produce a different frequency for each transmitter, ahorizontally polarized antenna system connected to said rst transmitter,a vertically polarized antenna system connected to said secondtransmitter, said polarizations representing the spatial location of thetransmitters, and means to alternately key said rst and said secondtransmitter by said push-pull oscillator.

ROSCOE H. GEORGE.

